Infratil is dropping hints it is in the running to buy a major London airport, although it insists there are better opportunities "closer to home".

In recent weeks there have been repeated reports from Britain that Infratil is part of a team bidding for Stansted Airport, north of London.

The team is believed to include Infratil's management company Morrison & Co as well as the NZ Superannuation Fund, with which it jointly owns Z Energy.

Infratil has never officially confirmed the reports although it is understood work has been done preparing a bid.

Ferrovial of Spain which owns the Stansted, has been forced to sell several British airports by the competition regulator. Expected to sell for around £1 billion ($1.94b) Manchester Airports Group, which owns several regional British airports, has been touted as the front runner in the process.

During a presentation of Infratil's half year results in the Amora Hotel in Wellington this morning, chief executive Marko Bogoievski said the company, majority owners of Wellington Airport, was looking at buying further assets in the sector, which could include Britain.

"We are looking at further airport [acquisition] opportunities and we wouldn't be adverse to the UK, so there's nothing generic about UK airports, it's more an airport by airport opportunity."

Asked whether Infratil was one of four short-listed bidders for Stansted, Bogoievski said: "We wouldn't know, would we?", appearing to imply a bid has been submitted.

The comments came as Infratil reported a $16.5 million loss for the six months to September 30, caused mainly by a $47m impairment on its British airports in Kent and the west of Scotland.

Attempts to sell the loss-making airports have been unsuccessful although the process was continuing.

Bogoievski said the airports, especially the Ryanair-dependent Prestwick in the west of Scotland, were purchased on the expectation of strong growth in low-cost travel, but had been exposed by both sector and economic changes.

"We'd be the first to accept that not all airports are created equally ... We had a strong top-down view about the way low-cost travel would evolve [between] point to point destinations in developed Europe, and that did play out for several years but then fundamental changes occurred."

The company has had a long heritage in the sector, having previously part-owned Auckland Airport, as well as airports in Perth and the Northern Territory in Australia.

"I think there's probably more convincing opportunities over time likely to emerge closer to home," Bogoievski said, referring to sales in emerging markets where Infratil would be interested in investing.

"You will see secondary assets sold as either state or local government authorities are forced to divest or privatise some of their assets or release funds for other services, particularly infrastructure."

Despite looking at an increasing number of possible businesses for sale during the period, no deals were concluded, with hints that it was being outbid by eager buyers.

"Investors without choices and facing an extremely low interest rate environment are more willing to 'pay up', even if it means then being locked into low returns," the company said in a statement sent to the NZX.

Bogoievski repeated that the next 12-18 months could be more active in terms of Infratil buying and selling assets, although he gave no clear signals of deals being imminent.

During the period of the results TrustPower, which is NZX-listed but majority owned by Infratil, began work on the $550m Snowtown II windfarm in South Australia. Bogoievski said the project was the largest Infratil had ever undertaken, and was projected to make an unleveraged return of more than 13 per cent.

The loss for the six months to September compared to a $50m surplus for the same period a year ago.

TrustPower, Wellington Airport, its Australian energy business and Z Energy, saw increased earnings over the same period a year ago.

NZ Bus, which operates public transport in Wellington and Auckland saw a drop which it blamed on an unflattering comparison to last year, which included Rugby World Cup.

Chief financial officer Kevin Baker said NZ Bus' earnings before interest, tax, depreciation, amortisation and financial instruments of $21.8m was around $4m below what the company had targeted.

"In an environment of low growth and vigorous competition these were pleasing outcomes and reflect good positioning and management," Infratil said in a statement to the NZX.

Despite the fall in profits Infratil said it would pay shareholders a dividend of 3.25 cents, an 8 per cent increase over a year ago, payable to shareholders on the register on November 30.